1. Field of the Invention
The present invention concerns an optical device suitable, for example, to display apparatus for conducting display of numericals or characters or X-Y matrix display, as well as an optical filter capable of controlling light transmissivity or light reflectivity in a visible light region (wavelength at 400 to 700 nm), as well as a fabricating method thereof, a driving method thereof and a camera system.
2. Description of the Related Art
An electrochromic display device employed in display apparatus such as digital watches (hereinafter simply referred to as xe2x80x9cECDxe2x80x9d) is a non-light emission type display device which conducts display by reflection light or transmission light as a light control device by electrochemical operation, so that it has a merit giving less feeling of fatigue even in long time observation, as well as a merit that if requires relatively low driving voltage and less consumption power.
For instance, as disclosed in Japanese Published Unexamined Patent Application No. Sho 59-24879, a liquid type ECD using organic molecule type viologen molecule derivatives that reversibly form states of coloration/color extinction as the electrochromic material (EC material) has been known. However, ECDs using the viologen molecule derivatives involve a problem that response speed or degree of shielding is insufficient. In addition, as a light amount control device, it is necessary that the light transmissivity can be controlled in a visible light vision (wavelength at 400 to 700 nm), and no sufficient characteristics can be obtained with the ECD material as described above.
In view of the above, the present inventor has noted on a light control device utilizing deposition/dissolution of a metal salt, instead of ECD, and has found that it can provide more excellent characteristics than the EC material with respect to the response speed and the degree of shielding in the course of research and development thereof.
While various metals salts can be used for such an optical device, those systems using deposition/dissolution of silver particles are excellent in view of optical characteristics. That is, an electrolyte is used as the material for a reversible plating, that is, RED (Reversible Electro-Deposition) in which a solution for the electrolyte shows no absorption spectrum in a visible light region (wavelength at 400 to 700 nm) upon preparation and causes deposition/solution of silver particles from a silver salt (including silver complex salt) capable of forming substantial uniform shielding in the visible light region upon coloration. Further, the silver salt has a possibility of deposition/solution by control for driving. Meanwhile, a cyan type solution has been used so far as a plating bath regarding deposition of silver particles from a silver salt but, since the cyan type solution is fatally poisonous, it is preferred to use a non-cyan type silver salt in the optical device of the present invention in view of safety for operation environment and discarding of liquid wastes.
Under the situations described above, it is possible to provide a non-light emitting type optical device such as an optical filter which consumes less electric power and which is suitable to a visible light region.
FIG. 1A and FIG. 1B, and FIG. 2 show a cell structure of an existent electrochemical light control device described above.
As shown in FIG. 1A and FIG. 2, a pair of transparent glass substrates 4 and 5 are disposed at a predetermined distance as a display window. As shown in FIG. 1A, working electrodes 2 and 3 each comprising an indium tin oxide (ITO) film obtained by doping tin to indium oxide are opposed to each other on the inner surfaces of the substrates 4 and 5, and an electrolyte 1 containing a metal salt dissolved therein is sealed between the opposed working electrodes 2 and 3. Counter electrodes 6 are disposed at the circumferential edges between the substrates 4 and 5 that function also as spacers, by which the sealed electrolyte 1 is sealed between the substrates 4 and 5.
In the optical device described above, when a DC driving voltage is applied for a predetermined period of time, as shown in FIG. 1B, between the counter electrode 6 as an anode and the working electrodes 2 and 3 as the cathode, metal ions dissolved in the electrolyte take place the oxidation/reduction reaction at the cathode as shown by the following formula (1):
Mn++nexe2x88x92xe2x86x92Mxe2x80x83xe2x80x83(1)
(n: natural number)
and the working electrodes 2 and 3 on the cathode change from transparent to colored states by deposited metal particles. FIG. 1B is a conceptional view illustrating the electrochemical mechanism in this reaction.
When the foregoing reaction is explained specifically to a case of using a silver salt solution as the electrolyte 1, a silver plate is used for the counter electrodes 6 and the silver salt solution is formed, for example, by dissolving silver bromide into dimethyl sulfoxide (DMSO). As shown in FIG. 1B when a DC driving voltage is applied for a predetermined period of time between the counter electrode 6 as the anode and the working electrodes 2 and 3 as the cathode, oxidation/reduction reaction is taken place for silver ions at the cathode as shown by the following equation (2):
Ag++exe2x88x92xe2x86x92Agxe2x80x83xe2x80x83(2)
and the working electrodes 2 and 3 on the cathode change from transparent to colored states by deposited Ag particles.
When the metal particles are deposited on the working electrodes 2 and 3 as described above, a specified reflection color with the deposited metal particles is observed through the display window. The filter effect due to the coloration, namely, the transmissivity for the visible light (or density of coloration) changes depending on the level of voltage or the application time thereof. Accordingly, the cell can function as a variable transmissivity display device or an optical filter by controlling the factors.
On the other hand, in a state where the cell is in the colored state, when a DC voltage is applied in the opposite direction between the counter electrode 6 and the working electrodes 2 and 3, the working electrodes 2 and 3 on which the metal particles are deposited now act as the anode to cause a reaction of the following formula (3):
Mxe2x86x92Mn++nexe2x88x92xe2x80x83xe2x80x83(3)
and Ag particles deposited on the working electrodes 2 and 3 are restored from the colored state to the transparent state.
This is to be explained to a case of using a silver salt solution for the electrolyte 1. When a DC voltage is applied in the direction opposite to the above between the counter electrode 6 and the working electrodes 2 and 3 in a state where the cell is in the colored state, the working electrodes 2 and 3 on which Ag particles are deposited now act as the anode to take place the reaction of the following formula (4):
Agxe2x86x92Ag++exe2x88x92xe2x80x83xe2x80x83(4)
and Ag particles deposited on the working electrodes 2 and 3 are restored from the colored state to the transparent state.
FIG. 3 and FIG. 4 show another electrochemical light control device of the prior art.
In this example, as shown in the cross sectional view of FIG. 3, working electrodes 8a, 8b, 8c, 8d, 8e and 9a, 9b, 9c, 9d, 9e each comprising a pair of ITO films are opposed to each other on the inner surfaces of a pair of transparent glass substrates 11 and 12 constituting a cell. Counter electrodes 7a, 7b each comprising a silver plate are disposed to the outer circumference of the outer working electrodes 8e and 9e. The substrates 11 and 12 are kept and sealed at a predetermined distance by a spacer 13 and an electrolyte 1 is sealed between the substrates.
As shown in a plan view of FIG. 4, the working electrodes 8a-8e and 9a-9e, and counter electrodes 7a and 7b are planer electrodes formed in a coaxial pattern. Each of the electrodes are paired as 8a with 9a, 8b with 9b, 8c with 9c, 8d with 9d, 8e with 9e and 7a with 7b, respectively, and connected to driving power sources 14a, 14, 14c, 14d, 14e and 14f by way of wirings 15a, 15b, 15c, 15d, 15e and 15f, respectively, each comprising fine chromium wires.
In this constitution, metal particles can be deposited from the electrolyte 1 on each of the electrodes as the anode and colored by applying a predetermined potential (V1, V2, V3, V4 and V5, V6 being a standard potential at the counter electrodes 7a and 7b) to each of the opposing pair of working electrodes 8a and 9a, 8b and 9b, 8c and 9c, 8d and 9d, 8e and 9e respectively. The filter effect by the coloration, namely, the transmissivity to the visible light (or density of coloration) changes with the level of the voltage or the application time thereof.
If V1=V2=V3=V4=V5, the cell can be colored uniformly over the entire region of the cell and the degree of density can be changed uniformly in accordance with the voltage or the application time thereof. Further, if it is determined as |V1| greater than |V2| greater than |V3| greater than |V4| greater than |V5|, the color density decreases from the central portion to the periphery (that is, transmissivity is increased). On the other hand, if it is determined as |V1| less than |V2| less than |V3| less than |V4| less than |V5|, the transmissivity is decreased from the central portion to the periphery and the constitution is useful as an optical diaphragm for use in CCD (Charge Coupled Device) such as of a television camera and since the size of the device can be reduced, it can sufficiently cope with increase for the integration degree of CCD.
By the way, in the existent electrochemical light control devices described above, a pure metal plate comprising the same kind of metal as the metal deposited/dissolved at the working electrode was used as it is for the counter electrodes 6, 7a, 7b. In this case, since the metal can be supplied smoothly from the electrolyte when the metal is deposited on the working electrode and, on the other hand, the metal can be absorbed rapidly to the electrolyte when the metal is dissolved on at the working electrode, the oxidation/reduction reaction of metal at the working electrode is advantageously conducted smoothly. Particularly, the above-mentioned merit is remarkable when a silver plate is used as the counter electrode in a case of using the silver salt solution for the electrolyte 1.
However, when a pure metal plate is used for the counter electrode, since the oxidation/reduction reaction is not uniform as the life of the device is increased, inactivated metal particles deposited on the counter electrode suspend in the electrolyte to contaminate the inside of the device and lower the transparency upon driving of the device, which may lead to a problem of lowering the transmissivity to the visible light or causing short-circuit between the electrodes.
For example, in the existent device shown in FIG. 3 and FIG. 4, upon color extinction of the working electrode, metal particles are deposited on the counter electrodes 7a and 7b as the cathode. In this case, since lines of electric force of the electric field are concentrated to the angled portion (edge) of the electrode, deposited metals are grown on the portion and relatively large metal particles are deposited/grown and detached from the edge. Different from fine particles of metal B deposited in a thin-film state at other portions near the edge, the particulate metal A (refer to FIG. 5) not easily dissolved upon coloration of the working electrode and, as shown in the figure, and is detached from the edge in an activated state as it is and suspended in the electrolyte 1. When such metal A is increased in the electrolyte, it lowers the transparency of the device upon color extinction of the working electrode and such metal particles also cause short-circuit between the electrodes to cause a significant problem that has to be dissolved when the metal plate is used as the counter electrode of the device.
For overcoming the foregoing problems regarding the counter electrode, one of the present inventors has proposed a counter electrode prepared by coating or printing a resin paste containing conductive particles such as of conductive carbon, silver, copper or nickel, on a current collector of the underlying layer instead of the existent counter electrode made of a metal plate. In this case, since the electrode can be formed into a shape with no substantial angled corner, local concentration of the electric field at the counter electrode can be moderated or prevented, whereby the problem of inactive metal particles relevant to the existent counter electrode can be overcome and an electrochemical light control device with a stabilized potential for the counter electrode and capable of stable driving can thus be attained (Japanese Patent Application No. Hei 10-009458).
However, when a carbon material is used, for example, as the conductive particles, adhesion between the conductive layer (resin layer containing the carbon material) of the counter electrode and the underlying layer (underlying electrode not electrochemically reacting with the electrolyte, that is, a current collector) as oxidation/reduction reaction of metal is repeated by a number of times at the transparent electrode and the counter electrode by driving the device and the conductor layer tended to be defoliated from the underlying layer. In such a state, the current collector is in direct contact with the electrolyte not by way of the layer of the carbon material and directly concerns reaction with the electrolyte. In this case, if the current collector is made of such a material that no smooth charge transfer is conductor to the electrolyte, it increases polarization resistance thereof extremely. Further, if the material allows relatively smooth charge transfer to the electrolyte, it causes deposition of silver or a silver-containing compound on the current collector or side reaction such as decomposition of electrolyte ingredients. Particularly, when the deposits are insulative, subsequent charge transfer can not also be conducted smoothly and, as a result, the polarization resistance is increased remarkably. Since such great polarization resistance not only causes large electric power consumption but also promotes the side reaction, it results in a problem of shortening the life of the device.
On the other hand, in the optical device such as the electrochemical light control device described above in the prior art, when the working electrodes 8a-8e, 9a-9e are operated as the anode and the potential thereof is polarized in the noble (+) direction in order to proceed the oxidation reaction at the working electrodes 8a-8e, 9a-9e, there was a problem that the ingredients of the electrolyte 1 are oxidized and denatured if polarization at the working electrodes 8a-8e, 9a-9e proceed excessively. Particularly, when a silver salt solution is used for the electrolyte, a supporting electrolyte is often dissolved for promoting the dissolution of the silver salt. In this case, the electrolyte 1 is colored probably mainly due to oxidation of anions dissolved as an electrolyte or support electrolyte in the electrolyte 1. For example, when iodine ions are contained in the anions of the electrolyte or support electrolyte, the electrolyte near the working electrode is colored yellow, probably mainly due to iodine (I2) caused by oxidation reaction of iodine ions (that is, 2Ixe2x86x92R I2+exe2x88x92). This gives undesired effects on the light transmissivity or reflectivity in the optical device to cause lowering of characteristics of the optical device and deteriorate the optical device.
In view of the above, it is necessary to detect and control the potential of the working electrodes 8a-8e, 9a-9e, thereby preventing coloration of the electrolyte. It is the same as the potential of the counter electrodes. However, the potential of the working electrodes 8a-8e, and 9a-9e in the electrolyte 1 can not but be detected as the potential difference relative to the counter electrodes 7a and 7b in the device constituted described above. As has been described above, the potential of the counter electrodes 7a and 7b changes as the polarization at the counter electrode increases due to repeating electrochemical reaction in the electrolyte 1. Accordingly, the potential of the working electrodes 8a-8e and 9a-9e in the electrolyte 1 can not be measured accurately and, as a result, it was impossible to control the potential of the working electrodes 8a-8e and 9a-9e. 
In view of the above, it is an object of the present invention to provide an optical device free from the defoliation as described above, enabling stable driving by stabilizing the potential of the counter electrode and, at the same time, capable of attaining low electric power consumption and improved life of the device, by using a specified material different from the existent material for the counter electrode of an electrochemical light control device utilizing deposition/dissolution reaction of a metal, as well as a method of fabricating the device.
Another object of the present invention is to provide an optical device such as an electrochemical light control device of a constitution capable of suppressing formation of inactive metal particles on a counter electrode, which may contaminate the inside of the device, as well as a fabrication method thereof.
That is, the optical device according to the present invention for overcoming the foregoing subject provides an optical device having working electrodes and counter electrodes in which an electrolyte is disposed in contact with both of the electrodes and light can be controlled electrochemically by controlling an electric field applied to the electrolyte, wherein
the counter electrode comprises a single layer or a laminate structure having at least two layers, the single layer or the first layer of the laminate structure which is present on the side of the electrolyte comprises a metal having a lower ionization tendency than the metal deposited/dissolved at the working electrode, and a second layer below the first layer comprises a metal or an oxide thereof different from that in the first layer.
Further, the present invention also provides a method of fabricating an optical device having a working electrode and a counter electrode in which an electrolyte is disposed in contact with both of the electrodes and light can be controlled electrochemically by controlling an electric field applied to the electrolyte, wherein the method comprises:
a step of depositing a metal having a lower ionization tendency than that of a metal contained in an electrolyte and deposited on a working electrode by means of a gas phase film forming method or a plating method or a sol-gel method on a substrate thereby forming a counter electrode material layer,
a step of forming the counter electrode by patterning the counter electrode forming material layer, and
a step of covering the circumferential edge or the periphery of the counter electrode with a shading layer.
The optical device and the fabricating method thereof according to the present invention have a prominent feature in that the counter electrode comprises a single layer or a laminate structure having two or more of layers in which the first layer comprises a metal element having an ionization tendency lower than that of the metal to be deposited/dissolved at the working electrode. For example, when the electrolyte is a solution containing a silver salt dissolved therein, the first layer comprises palladium, platinum or gold that is a metal having an ionization tendency lower than that of silver. Further, the second layer below the first layer comprises a metal different from the first layer (for example, titanium, chromium or tungsten) or an oxide thereof (for example, indium-tin oxide prepared by doping tin to indium oxide (hereinafter simply referred to as ITO)) or tin oxide.
This will be explained with reference to a relation between the ionization tendency of the metal and the standard electrode potential shown below. In most cases, the standard electrode potential means a potential of an electrode material based on a normal (or standard) hydrogen electrode (NHE or SHE) at a standard pressure of a hydrogen gas of 1 atm and the value varies depending on temperature. Several standard electrode potentials in metal electrode reactions arranged orderly from negative values are referred to as electrochemical series. The following table shows metal series based on electrochemical series for main metals and standard electrode potentials thereof (at 25xc2x0 C.).
The standard electrode potentials correspond to potentials exhibited when the materials are dipped an aqueous solution (referred to as dipping potential, rest potential or natural potential) and those metals showing high dipping potentials are referred to as noble metals and those metals showing low potentials are referred as basic metals. Further, while a standard electrode potential in a non-aqueous solution system is usually different from that in the aqueous solution system, the relation regarding the level of the standard electrode potential in the non-aqueous system substantially corresponds, in most cases, to that in the aqueous solution system. This is the same, for example, to metal oxides. Then, the degree of the ionization tendency as a measure for the ease of ionization corresponds to the level of the standard electrode potential. That is, a material showing a lower standard electrode potential has a higher ionization tendency, whereas a material having a higher standard electrode potential has a lower ionization tendency. Then, it is assumed in this invention that xe2x80x9clow ionization tendencyxe2x80x9d means high standard electrode potential.
The same thing can be applied to metal compounds such as ITO or tin oxide. For example, ITO, In:Sn ratio of which is 9:1, is 0.4V more noble relative to silver in a variety of aqueous or non-aqueous solutions. Therefore, the standard electrode potential of the ITO is about+1.2 V vs. NHE.
In the optical device, a material having a more noble potential than the metal to be deposited/dissolved at the working electrode is used for constituting the first layer of the counter electrode in contact with the electrolyte. For example, in a case of using a silver salt solution for the electrolyte, the first layer for the electrode is constituted with a metal having a more noble potential than metal silver (Ag). That is, as can be seen from the table described above, any of metal such as Ag, palladium (Pd), platinum (Pt) and gold (Au) having lower ionization tendency than hydrogen is a noble metal having a positive potential with reference to the standard potential (0V) of hydrogen. In addition, since the positive potential of the metal used for the first layer is higher than that of silver, Pd, Pt or Au showing a lower ionization tendency than that of Ag is referred to as a metal having a more noble potential than Ag. For example, metals having higher ionization tendency than hydrogen, for example, Li, Al, Ni, Sn and Pb can be said to be metals having basic potential with (xe2x88x92) potential with reference to the hydrogen standard potential (0V).
A metal having a lower ionization tendency (referred to as D) than the metal to be deposited/dissolved at the working electrode (referred to as C), has such a nature that deposition/dissolution reaction of the metal C at the surface proceeds reversibly and smoothly and polarization resistance at the counter electrode is not increased so much even if deposition/dissolution reaction of the metal C is repeated on the working electrode. As a result, this is stable, can suppress the polarization resistance at the counter electrode upon driving of the device the electric power consumption can be reduced and, in addition, contamination caused by side reactions on the counter electrode can also be suppressed.
This is particularly remarkable in a case where the metal C is silver and the metal D is platinum, palladium or gold. In a case where the carbon material or the like is used for the counter electrode, since silver is deposited from the inside of the counter electrode or silver is incorporated into the counter electrode during driving to change the constitution of the counter electrode and show a potential different from that in the initial stage, making it sometimes difficult to control driving. However, if the counter electrode is constituted with palladium, platinum or gold, they are formed uniformly as a dense thin-film by a gas phase film forming method or a plating method or a sol-gel method, by which obstacles are not intruded into the counter electrode, the potential for the counter electrode is not disturbed and the potential of the electrode is stabilized as described above during driving.
Therefore, according to the present invention, in an electrochemical light control device utilizing the metal deposition/dissolution reaction for instance, when a metal D having a lower ionization tendency than a metal C to be deposited/dissolved at the working electrode (or metal showing more noble potential than metal C) is used for the first layer of the counter electrode, the metal D in the first layer is less ionized than the metal C and smoothly proceeds deposition/dissolution reaction of the metal C on the surface of the metal D, so that the device is electrochemically stable, polarization at the counter electrode upon device driving can be suppressed and electric power consumption can be reduced, as well as contamination due to side reaction at the counter electrode can be suppressed.
In the present invention, the counter electrode comprises a single layer or a first layer of a metal having a lower ionization tendency than that of the metal to be deposited/dissolved at the working electrode (platinum, palladium or gold in a case of using a silver salt solution for the electrolyte), and the layer may be formed of a single species of material or two species of materials (which may be an alloy or a mixture), or the first layer may be a laminate of metals selected from those metals having lower ionization tendency than the metal to be deposited/dissolved at the working electrode.
Further, according to the present invention, the counter electrode is covered with a layer of a metal having a lower ionization tendency that of the metal to be deposited/dissolved at the working electrode and adhered favorably with a substrate by way of a second layer comprising a metal or an oxide thereof different from that of the first layer. The second layer is not necessary if adhesion is favorable between the first layer and the substrate. However, if the adhesion is not satisfactory in view of the matching between the materials, the adhesion between the counter electrode and the substrate can be ensured to stabilize the potential of the counter electrode by disposing a material having a satisfactory adhesion to both of the first layer and the substrate as a second layer.
Further, when a layer of the metal element D having a lower ionization tendency than that of the metal C to be deposited/dissolved on the surface of the working electrode is disposed as the first layer of the counter electrode and, further, a material containing the metal C is formed as a third layer on the surface thereof, the dipping potential of the counter electrode when dipped in the electrolyte is identical with that of the metal C and is stabilized as well. Then, as described above, since deposition/dissolution reaction of the metal C on the surface of the metal D is conducted smoothly, polarization resistance at the counter electrode can be suppressed to ensure the performance of the optical device.
In any of the cases described above, since the surface of the counter electrode is not coated with a resin paste layer containing the conductive particles as described above but formed with the same kind of metal as the metal to be deposited/dissolved at the working electrode or a metal having a lower ionization tendency, the metal layer can be formed with good adhesion by a gas phase film forming method or a plating method or a sol-gel method, so that when it is dipped in the electrolyte, or even during driving in the electrolyte, it is not defoliated or separated and increase of the polarization potential can be suppressed.
Further, in the counter electrode comprising the single layer or the laminate structure, since the first layer can be formed by the gas phase film forming method or the plating method or the sol-gel method, it can be formed in a thin film state compared with the case of constituting the entire counter electrode with a metal plate or the like, so that the end edge of the counter electrode is formed into such a shape as less causing an angled corner (edge) as shown in FIG. 5.
Accordingly, when immersing and driving the counter electrode in the electrolyte, local concentration of electric fields can be moderated or prevented and deposition of inactive particulate metal on the counter electrode can be suppressed or prevented effectively. As a result, lowering of the transparency of the device or short circuit between electrodes caused by suspension of the inactive metal particles in the electrolyte which could not be prevented in the existent device can be suppressed or prevented effectively.
A further object of the present invention is to provide an optical device such as an electrochemical light control device capable of detecting and controlling the potential of the working electrode or the counter electrode accurately, as well as a fabricating method thereof and a driving method thereof.
In the optical device according to the present invention, a reference electrode having no direct concerns with reversible electrolytic deposition on the surface of the working electrode is disposed in contact with the electrolyte. The reference electrode, being in contact with the electrolyte, always shows a constant dipping potential. Accordingly, by detecting the potential difference between the reference electrode and the working electrode or the counter electrode, the potential of the working electrode or the counter electrode can be obtained from the detection potential difference also when oxidation/reduction is taken place in a state being dipped in the electrolyte.
The reference electrode in the present invention may be formed as a single layer or a laminate structure having two or more of layers in the same manner as the counter electrode but, since only a minute current flows for the measurement and monitoring of the potential for the working electrode and/or the counter electrode and no violent oxidation/reduction reaction occurs as done at the working electrode or the counter electrode, the constituent material for the first layer can be selected from a wider range than that for the counter electrode. That is, any of materials that is not dissolved when dipped in the electrolyte and shows a constant stable dipping potential can be used in principle. In view of the stability in a state in contact with the electrolyte, the first layer of the reference electrode is preferably constituted with the same kind of metal as the metal to be deposition/dissolved at the working electrode upon driving of the optical device, or a metal having a lower ionization tendency than the metal. With such a constitution, even when the reference electrode is dipped in the electrolyte, the first layer is chemically stable and not dissolved spontaneously into the electrolyte and the reference electrode shows a constant dipping potential. Therefore, the potential for the working electrode or the counter electrode can be detected more accurately based on the stable potential of the reference electrode.
In a case of the laminate structure having two or more layers, a second layer is disposed between the first layer and the substrate like that in the case of the counter electrode described above if the material constituting the first layer has no satisfactory adhesion with the substrate material or if electric connection with the lead electrode to the reference electrode is not satisfactory. When such a second layer is disposed, adhesion of the reference electrode as the substrate can be ensured to stabilize the potential of the reference electrode.
Further, when a layer of a material having a lower ionization tendency than the metal to be deposited/dissolved on the surface of the working electrode upon electrolytic deposition is disposed and a substance containing a metal to be deposited/dissolved on the surface of the working electrode is disposed on the surface to constitute a third layer, the potential of the reference electrode upon dipping into the electrolyte is equal with the potential of the material to be deposited on the surface of the working electrode and stabilized. Also in this case, the potential of the working electrode or the counter electrode can be detected more accurately based on the stable potential of the reference electrode.
Since the reference electrode is used for measuring and monitoring the potential of the working electrode and/or the counter electrode, no large current flows as in the counter electrode, and the third layer can be constituted with a conductive particle layer containing particles of a metal to be deposited/dissolved on the surface of the working electrode. Also in this case, the potential of the working electrode or the counter electrode can be detected more accurately based on the stable potential of the reference electrode. Further, if the electric connection of the conductive particle layer constituting the third layer with the lead electrode to the reference electrode is not satisfactory, a first layer is disposed as the current collector layer below the third layer. Further, if adhesion with the substrate material is not satisfactory, a second layer as an adhesion layer is disposed between the third layer and the substrate. The first layer and the second layer may be formed separately or the first layer may be used also as the second layer. In any case, by the provision of the first layer or the second layer, electric connection and adhesion of the reference electrode with the substrate can be ensured to stabilize the potential of the reference electrode.
Further, the present invention also provides a method of fabricating an optical device having a working electrode and a counter electrode, as well as a reference electrode in which an electrolyte is disposed in contact with the electrodes and light is controlled electrochemically by controlling a voltage applied to the working electrode and the counter electrode relative to the reference electrode, in addition to the same method as that for forming the counter electrode described above, the method comprising:
a step of depositing a transition metal or a conductive metal oxide on a substrate by way of a gas phase film forming method or a plating method or a sol-gel method, thereby forming a reference electrode collector layer,
a step of patterning the reference electrode collector layer, thereby forming the reference electrode collector,
a step of covering the portion of the reference electrode collector with a conductive particle layer, and
a step of covering the circumferentially edge or peripheral portion of the reference electrode current collector with a shading layer.
Further, the present invention also provides the optical device described above in which an external circuit having a limiter for controlling an external power source is preferably provided for keeping a potential difference between the working electrode and the reference electrode within a predetermined range.
Provision of the limiter can keep the potential of the working electrode within a predetermined range to suppress excess polarization at the working electrode. Therefore, undesired effect of the excess polarization at the working electrode on the materials in the electrolyte can be prevented. Specifically, coloration of the electrolyte assumed to be attributable mainly to the oxidation of anions in the electrolyte or supporting electrolyte caused by excess polarization at the working electrode can be prevented.
Further, the present invention also provides a method of driving an optical device for controlling light by reversible electrolytic deposition from an electrolyte to the surface of a working electrode disposed on a substrate, wherein the method comprises disposing a reference electrode having no direct concerns with electrolytic deposition/dissolution between the electrolyte and the working electrode and/or the counter electrode, detecting a potential difference between the reference electrode and the working electrode and/or the counter electrode, and controlling current supply to the working electrode and/or the counter electrode upon reversible electrolytic deposition to the surface of the working electrode and/or the counter electrode so as to keep the potential difference within a predetermined range.
According to the driving method for the optical device described above, since the potential difference between the reference electrode and the working electrode is detected, the potential of the working electrode when dipped in the electrolyte is detected based on the reference electrode showing a constant dipping potential when dipped in the electrolyte. Then, since the current supply to the working electrode is controlled so as to keep the potential difference within the predetermined range, excess polarization at the working electrode during current supply is suppressed. Therefore, light can be controlled by reversible electrolytic deposition from the electrolyte to the surface of the working electrode while preventing undesired effects caused by excess polarization at the working electrode on the substances in the electrolyte.
Then, the present invention further provides a camera system mounting an optical device therein. Since the optical device is excellent in the optical characteristic and can be driven stably, the reliability of the camera system can be enhanced as well. Further, according to the camera system, since the optical device utilizing the electrochemical reaction is mounted and portions of the device can be reduced in the size compared with the existent case, the size of the camera system itself can also be reduced.